Extreme ultraviolet lithography (EUV, also known as soft x-ray projection lithography) is a contender to replace deep ultraviolet lithography for the manufacture of 0.0135 micron, and smaller, minimum feature size semiconductor devices.
However, extreme ultraviolet light, which is generally in the 5 to 100 nanometer wavelength range, is strongly absorbed in virtually all materials. For that reason, extreme ultraviolet systems work by reflection rather than by transmission of light. Through the use of a series of mirrors, or lens elements, and a reflective element, or mask blank, coated with a non-reflective absorber mask pattern, the patterned actinic light is reflected onto a resist-coated semiconductor substrate.
The lens elements and mask blanks of extreme ultraviolet lithography systems are coated with reflective multilayer coatings of materials such as molybdenum and silicon. Reflection values of approximately 65% per lens element, or mask blank, have been obtained by using substrates that are coated with multilayer coatings that strongly reflect light within an extremely narrow ultraviolet bandpass; e.g., 12.5 to 14.5 nanometer bandpass for 13.5 nanometer extreme ultraviolet (EUV) light.
There are various classes of defects in semiconductor processing technology which cause problems. Opaque defects are typically caused by particles on top of the multilayer coatings or mask pattern which absorb light when it should be reflected. Clear defects are typically caused by pinholes in the mask pattern on top of the multilayer coatings through which light is reflected when it should be absorbed. And phase defects are typically caused by scratches and surface variations beneath the multilayer coatings which cause transitions in the phase of the reflected light. These phase transitions result in light wave interference effects which distort or alter the pattern that is to be exposed in the resist on the surface of the semiconductor substrate. Because of the shorter wavelengths of radiation which must be used for sub-0.0135 micron minimum feature size, scratches and surface variations which were insignificant before now become intolerable.
The problem that the thin absorber addresses is the shadowing issues seen with thicker absorbers as the pattern gets smaller, which ends up limiting the size features that can be printed on a substrate. Achieving a thinner absorber requires using new materials that absorb 13.5 nm light better than the current absorbers in use.
In view of the need for the increasingly smaller feature size of electronic components, it is increasingly critical that answers be found to these problems. In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations, it is critical that answers be found for these problems. Additionally, the need to reduce costs, improve efficiencies and performance, and meet competitive pressures adds an even greater urgency to the critical necessity for finding answers to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.